The present invention relates to piston compressors.
The invention can most advantageously be realized in refrigerator piston compressors operating on various refrigerants, including aggressive and explosive agents, such as freon, ammonia, propane, etc., and in compressors wherein the displacement is controlled through disconnection of several cylinders at a time, and, particularly, through disconnection of cylinders in pairs.
These are already known in the art compressors incorporating capacity regulators, wherein the displacement is controlled by lifting the suction valves in several cylinders simultaneously by the use of a hydraulic or a pneumatic drive.
Thus, the GRAT company of Denmark builds piston compressors for refrigeration units, wherein the displacement is controlled by a regulator incorporating movable spring-loaded bushings mounted on the outer surfaces of the cylinder sleeves. Lifters built into the top section of the movable bushings act upon the suction valve ring disks.
The movable bushings are mechanically linked in pairs with horizontal rods bearing the loads due to the force exerted by a lifting spring and the oil pressure built up in the distribution unit. The spring and the unit are arranged on the compressor body between the cylinders.
With no oil pressure produced in the distribution unit by the compressor oil pump, the lifting spring displaces the horizontal rods to the upper position, and the rods in turn drive the movable bushings and the lifters, with the result that the disks in the suction valves of both cylinders are lifted. Thus, the compressor operates at a lighter duty due to bypassing of the gas from two cylinders simultaneously into the compressor suction chamber.
When an oil pressure is applied to the distribution unit, the force exerted by the lifting spring is balanced by the oil pressure. The movable bushings and the lifters acted upon by their own springs are caused to move downward, and both cylinders start operating.
The method whereby the piston compressors employ hydraulic or pneumatic lifting of the suction valve disks in groups (in particular, in pairs) for changing the compressor capacity permits simplification of the displacement regulation system and of the compressor as a whole.
However, the compressors incorporating the above-mentioned units have a number of disadvantages. It is a known fact that the response of the hydraulic drives is rather slow and that the use of mechanical lifters actuating the suction valve disks is detrimental to the reliability both of the capacity regulation unit and to the suction valve disks which fail quite frequently.
In addition, the use of the hydraulic drives in the piston compressor capacity regulation systems necessitates an increase in the power of the compressor oil pumps to produce a pressure sufficient for lifting the disks, and further development of special-purpose instruments and mechanisms to control the capacity regulation units.
Apart from whose compressors, the displacement is regulated by the units through hydraulic or pneumatic lifting of the suction valve disks, there are known compressors furnished with regulation units incorporating electromagnetic drives.
Thus, there is known in the art a piston compressor in which the capacity regulation unit comprises one or two electromagnet coils used to actuate one or two suction valve disks. The electromagnet coils are located either in the refrigerant medium, or are isolated from it by a coil casing and a screen made of nonmagnetic material. The travel of the suction valve disks is restricted by the disk travel limit stops which at the same time function as electromagnet poles. With an operating voltage applied to the coil winding, a magnetic field is produced, which is closed through a magnetic circuit passing through the suction valve disks, and thereby, causes the disks to thrust against the disk travel limit stops. The gas contained in the cylinder is bypassed to the suction chamber through the open suction ports.
Thus, there is known a prior-art piston compressor, whose capacity regulation unit comprises one or two electromagnet coils used to actuate one or two suction valve disks. The electromagnet coils are mounted either in the refrigerant medium, or are isolated from it by a coil casing and a screen made of nonmagnetic material. The travel of the suction valve disks is restricted by the disk travel limit stops which at the same time function as the electromagnet poles. With an operating voltage applied to the coil winding, a magnetic field is produced, which is closed through a magnetic circuit passing through the suction valve disks, and thereby, causes the disk to thrust against the disk travel limit stops. The gas contained in the cylinder is bypassed to the suction chamber through the open suction ports.
Compared to the piston compressors wherein the hydraulic or pneumatic drives are used to control the displacement, the piston compressors with the foregoing electromagnetic regulation units are distinguished by practically instantaneous response and by freedom from auxiliary intermediate components (such as the lifters) serving to actuate the valve disks. However, the piston compressors furnished with electromagnetic capacity regulators also suffer from a number of disadvantages.
In particular, tightness of the electromagnet coil in the capacity regulators of said compressors cannot be guaranteed, hence, the regulator cannot be used where explosive and corrosive agents are employed. Location of current-carrying lines inside the compressor and the use of electrode seals add to the impracticability of said regulators when aggressive and explosive agents are handled, and the compressor construction is fairly complicated. To replace a coil in case of failure, the compressor must be stopped, unsealed and subjected to partial disassembly.
The attempts to eliminate the above disadvantages have led to development of a new piston compressor, whose the capacity regulator comprises an electromagnet coil which actuates the suction valve. The coil is arranged on the outer side of the compressor body, and is connected to the suction valve by a magnetic circuit. The magnetic circuit is formed by the compressor body, by the cylinder and by the pressure valve body.
The attempts to eliminate the above disadvantages have led to development of a new compressor, whose capacity regulator comprises an electromagnet coil which actuates the suction valve. The coil is mounted on the outer side of the compressor body, and is connected to the suction valve by a magnetic circuit. The magnetic circuit is formed by the compressor body, by the cylinder and by the pressure valve body.
The suction valve is retained in the open position by force, and, hence, the cylinder is allowed to discharge when the supply voltage is applied to the electromagnet coil. The magnetic flux directed through the magnetic circuit is closed via the body of the suction valve. The resulting magnetic force lifts the disk of the suction valve.
A piston compressor incorporating said regulator provides for absolute tightness of the coil winding so that the compressor can be operated with explosive and aggressive agents, no stoppages and unsealing are required for replacement of the electromagnet coils, and the construction is simplified by utilizing the compressor parts and assemblies for completion of the magnetic circuit.
Yet, in the piston compressor provided with the prior-art capacity regulation unit, and also in the compressor provided with the regulator proposed by the German patent No. 636470, each compressor cylinder discharges through the use of an individual electromagnet coil, whereby simultaneous actuation of several suction valves of different compressor cylinders is not possible.
As a consequence, the compressor construction is complicated, plenty of wire is required, and the compressor dimensions and weight increase.
It is an object of the present invention to simplify the construction of the piston compressor by modifying the compressor capacity regulator capable of changing the compressor displacement by operating a group of cylinders actuated by a single electromagnet coil.
Another object of this invention is to reduce the weight of the piston compressor by virtue of reduced dimensions and reduced weight of the capacity regulator.